I was just mousing around at archive.org and found an interesting rarity called The Private Life of Rochester Van Jones. Yes, it's that Rochester. Apparently, Jack Benny's valet came very close to getting his own spinoff show. Unfortunately, CBS didn't pick the show up so all there is of what might have been is the two-part audition show.

Amazingly for something so rare, the recording is absolutely pristine. It's really hard to believe that it dates from 1950.

I'm betting the recording is so good because it wasn't a broadcast recording, but a direct recording. IE: many of these shows we're listening to, even some of the best quality, are actually recordings of broadcasts, probably made at local radio stations. The Rochester recording was probably made directly to tape or disk in a network studio, and lingered in their archives for ages until being discovered.